Optical analysis of the behaviour of a salt-gradient solar pond

The three-zone salt-gradient solar pond is a body of saline water that collects solar radiation and stores it in the water as thermal energy. The performance of solar ponds largely depends on the portion of solar radiation which reaches the bottom region (LCZ) and from which heat is extracted subsequently. An analysis is made to determine the form of the attenuation of the solar rays inside the pond as a function of wavelength and depth, taking into consideration that each zone has its extinction coefficient due to its salt concentration. Insertion of partitions between zones (between the UCZ and NCZ and between the NCZ and LCZ) has also been discussed. Equations describing the transmissions and reflection coefficients in the presence of partitions were derived. The portion of the solar energy that is absorbed by the different depths of NCZ has been calculated for Cairo. About 20% of the incident radiation is absorbed by the NCZ, and with the presence of transparent partitions this quantity decreases by about 20%.